Separation of phenols from thiophenols



Patented Nov. 15, 1949 irF Fil'iCf-E SEPARATION 9F PHENGLS ,FROIVI THIOPHENOLS of Ohio No Drawing. Applicationseptember 2%,..1948, Serial No. 51,123

19 Claims. "1 This invention relates to a method of separating phenols from thiophenols and, in particular, it relates to an adsorption process of separating phenols from thiophenols whichhave' closely related structures.

This application is a-continuation-inpart of my'application Serial Number 547,989, now abandoned, filed August 3, 1944.

Phenols recovered from 'coaltars and petroleum oils are frequently admixed with thiophenols which occur naturally in the same media and because of the chemical similarity .of the two types of compounds, separation is very dimcult when purely chemical means are used. This in particular is "true when phenols are extracted virom their.naturallmedialbylmeans of causticalkali solution. A common source of mixtures of phenols and thiophenols is the alkaline prewash used in refining cracked gasolines. Quitegenersally in such operations, ;an ;acid oil fraction is sprung .from the :alkaline was-h solution, which jfraction-hassa boiling :range ::from about 359 to about 450311, land-1a desirable cresol content. However, the economic valuev of the material --is seriouslyrreducedbecause it contains thiophenols Zin substantial :amounts.

Accordingly, itnis :a fundamental 1 object of the :instant invention toprovide .armethod which can serve as abasisforla-processcfor separating;phenols. from thiophenols and serve totconcentrate a :mixture :of :the compounds ;into fractions relatively :richer :in phenol and thiophenol, respectively.

;It is :asecond :object of the:invention to provide an adsorption'process-jfor the separation of aphenols from ;thiopheno1s.

lt isianother-gobject of theinvention to provide a-cmethod of'recovering a useful;phenol fraction :Irom .acid zoiil.

Ii'have discovereclsthatrelatively pure phenols can be separated from :mixtures :of-pheno-ls :and "thiophen'ols ;by;contactir.g ;the jnixtures with zsilica gel aatordinarytemperatures. Mixtures "-of phenol and thiop'henol- :which :are zrathericlosely related instructurebyyirtue ofrhavingesubstam "tially similar 'substituents onithe respective benzene rings are readily-separated,'=for the'phenols are preferentiallyadsorbed on silica gel'and oan be extracted therefromby using a-suitable solvent from which theycan be recovered. "'The process is applicable generally 'to mixtures oi -aromatic compounds-of carbon, hydrogennoxygen and sulfur, the on e group-of compounds:containing oxygen and the other group in the mixture :containing sulfur, wherein the oxygen andsulfur are at- :tached clirectly to: the nucleus.

In accordance :withmy invention, I prefer to filter the'mixture of a phenol and thiophenol 5 :through a bed of-silicagel until analysis: of the efiluentliquid or 'filtratesshows that phenol isl-no longer being adsorbed aonthe-silica gel as indicated lby-lthe fact that'theeffluent has substantially thesamercomposition as thezcharge. The asijlicargel-bed isitheniwashed with "a suitable-solvent, preferably 'a1.low'-'boiling hydrocarbon sol- =.vent, such as hexaneflbenzene or hydrocarbons fbo'iling :in the-gasoline range, capable-of remov- 1mg unadsorbed :materiali held in the :filter bed, 15111115 incapable of rextractingthe adsorbed con- :istituents :from :the :silica gel; Following ithis washing, the adsorbed phenols a-raextracted from the silica gel by means ofasuitable solvent, preferably a low-boiling 'ketone, such as acetone, butanone, or pentanone. Any hydrocarbon solvent boiling up to approximately 200,C.,is suitable-Ior thepreliminary washing of the silica gel and any "aliphatic ketone 'boiling "up to approximately 200C. is suitable for the extraction of the phenols from the silica gel.

To apply the process to a specific-mixture-of phenols anclthiophenols, consideration should'be given to the possibility that the phenol to be recovered may be substituted'to such an-extent that ;it .will not be adsorbed preferentially. I have .zfound that if .thesphenol to berecovered'from ad- ;mixture with1anthiophenol is soluble in sodium lhydroxidezsolution .of :a concentration about :10 per cent :.by weight, it will be preferentially adsorbed from admixture with very closely related athiophenols. :fIlhezsolubilitynof the phenol in any zalk'altmetal hydroxidesolutioncan be used, for iexample sodium, ipotassium, lithium, rubidium, ,iforitiistheccapacity of the phenol-t0 form pheenolatewhich is beingrrtested, :becauselit is those :yvhich xform 531K811 zphenolates which are readily adsorbed. In general, .imsu-bstitutedphenols will be adsorbed from admixture with unsubstituted thiophenols; 'likewisa'sub'stituted phenols will be adsorbedzfrom admixture with substitute'rlthio- -,phenols. 2 It iswhen a substituted phenol is to be recovered from admixture with unsubstituted thiophenol that the degree of substitution of the phenol or the degree of difierence'betweenthe ,structuresof the compounds should be considered. If the phenol is soluble in sodium hydroxide solution .of about 10 percent concentration, itwill bepreferentially adsorbed by silicagel.

'As an "example 'of the above procedure, the separation of thiop'hen'o'l from 2,4,G-tertiarybutyl phenol might be attempted. Because the hydroxyl group on the 2,4,6-tertiary butyl phenol is so hindered by alkyl groups, the thiophenol would be preferentially adsorbed. The 2,4,6-tertiary butyl phenol has no significant solubility in 10 per cent sodium hydroxide solution. However, 2,4-tertiary butyl phenol can be preferentially adsorbed from a mixture thereof with thiophenol and it is found to be readily soluble in 10 per cent sodium hydroxide solution.

Thus, the application of the process to the recovery of phenols from thiophenols as they occur in admixture, is well exemplified in the rendering of acid oils. These oils as they are sprung from spent caustic, may contain very lowboiling aliphatic acids, but will include phenolic and thiophenolic compounds of closely related structures in the fraction boiling from about 300 to 450 F. The phenolic bodies are easily recovered by successive adsorptive fractionations carried out with silica gel in accordance with the instant invention as illustrated by the following examples in which the separation of mixtures representing typical acid oil cuts is illustrated.

In order to demonstrate the invention, 125 grams of silica gel having a mesh size of approximately 8 to 14 was packed in a glass tube. The silica gel occupied a volume of 200 milliliters. Two hundred (200) grams of a mixture, containing 25 per cent by weight of meta-thlocresols and 75 per cent by weight of mixed metaand para-cresols was percolated by gravity at room temperature through the bed of silica gel at the rate of 1.3 barrels per ton per hour. The filtrate was divided into seven separate equal cuts and each was analyzed for thiocresols. The data are given in the following table:

TABLE I Per Cent by Per Cent by Per Cent by Cut No. Wgt. of Wgt. of Wgt. of Charge Thiocresol Cresols TABLE II g g Per Cent by Per Cent by Solvent sdVegnflFtee Wgt. of Wgt. oi Extract Thiocresols Cresols Hexane 31. 5 24. 6 75. 4 Acetone 17. 5 2. 4 97. 6

It is apparent from Table II that 17.5 per cent by weight of the original charge or 35 grams of cresols were recovered, containing 97.6 per cent by weight of cresols and 2.4 per cent by weight of thiocresols. Measured in terms of barrels of cresols per ton of silica gel, the yield was 1.6 barrels per ton. The cresols obtained were slightly better in quality than commercial cresols marketed by a well-known company. Commercial cresols, with which a sample pre-- pared in accordance with my invention was compared, contained 2.6 per cent of thiocresols.

The cresols from the first extraction were again percolated through the silica gel and four cuts of filtrate were taken and analyzed for thiocresols. The data on these four cuts are given in Table III:

TABLE III Per Cent by Wgt. of

Per Cent by W gt. of

Thiocresol Per Cent by W gt. of

Charge Hwww I-CRHD- caDcow otocozo F ST? a ap-q The silica gel was then washed with 200 milliliters of hexane to wash it free of unadsorbed material and thereafter washed with 150 milliliters ci acetone to extract the adsorbed ma- It will be seen from the table that 11 per cent of the initial charge of 35 grams containing 97.6 per cent of cresols and 2.4 per cent by weight of thiocresols was obtained as cresols having a purity of 98.6 per cent by weight.

It will be apparent that larger yields of cresols may be obtained by recontacting any or all of the filtrate cuts with silica gel. For example, the process can be carried out in series with the filtrate from one filter bed passing through successive filter beds followed by separate extraction of each bed with hydrocarbon solvent and ketone. In this manner it is possible to obtain a series of fractions of cresols of gradually decreasing purity from each bed and these fractions can be again treated in a series of contact steps with silica gel to increase the purity thereof. After contacting mixed phenols and thiophenois with silica gel, followed by extraction with hydrocarbon solvent and ketone, silica gel can be re-used for further treatment of phenol-thiophenol mixtures.

In additional testing of the process, a mixture of phenol and thiophenol containing 25 per cent by weight of thiophenol and per cent by weight of phenol was subjected to the adsorption process. A column of silica gel containing grams of 200 mesh activated silica gel was maintained at a temperature of about 110 F. in order to insure the retention of the percolating mixture in the liquid phase. One hundred (100) milliliters (approximately grams) of the blend of phenol and thiophenol was added to the column and subjected to a pressure of 6 pounds per square inch gauge of nitrogen. Frac- 'tions :of effluent were collected "and their volume :and weight recorded as follows:

Fractions ofthe efiluent from 'the column were .takenafter the intervals indicated and after the third fraction had been taken, nitrogen commenced issuing from the column. At this point, the test was ended, nitrogen pressure released, andheating discontinued. One hundred (100) milliliters of redistilled commercial hexane was "introduced into the top of the column at "70 Eundera pressure of p'ounds'per square inch gauge of nitrogen and 1:05 milliliters of liquid collected from the column before nitrogen again began to issue therefrom. Following the same technique, "76 milliliters of acetone was passed 'into the column under a pressure of 6 pounds .per square .inch gauge of nitrogen and during a period of four hours 190 milliliters of eliluent was collected. The hexane and acetone solutions thus recovered were separately distilled in the absence of air and the residues weighed. They were also analyzed for phenol and thiophenol with thefollowingresults:

TABLE VI Distribution of thiophenol and phenol [From acid-base titration usingphenolphthalcin indicator] Original charge was approximately 105 grams, so there was apparently a loss of some 12.5 grams (probably due to hold-up). Per cents are calculated on basis of 105 gram charge.

From these data, the figures showing the phenol content of the acetone extract, it was determined that about 2s per cent of the phenol present in the original mixture charged to the silica gel adsorption column was recovered in a state of about 99 per cent purity and that approximately 19 per cent of the thiophenol present in the mixture charged to the column was recovered with a purity of approximately 93 per cent.

Contact between the material undergoing treatment and the silica gel may be by contact filtration or percolation. Where percolation is used, upward or downward percolation may be practiced and the contact may be carried out at atmospheric pressure or at superatmospheric pressure.

The process as has been pointed out is particularly useful for the separation of phenols and thiophenols of closely related structure which would have substantially similar boiling points and reactivities and, therefore, complicate chemical processes for separation. By basing the process on the difference in adsorptivity of the has compounds, as shown, it is possible to develop an appreciable concentration of the phenol in a-given fraction by means of a single pass through an adsorption bed. As an empirical testof the type 0f phenol which "can be separated from a thiodegree of hindranceof the hydroxyl-group in the phenol should be about the same as the degree of hindrance of the sulfhydryl group in the thiophenol. If the structures are verydifierent, the one compound being relatively unsubstituted and the other carrying many hydrocarbon substituents, 'it is quite-possible that the difierenceinadsorptivity between the compounds will be-altered to the point that the polarities will change.

For example, a very highly substituted phenol, such as 2,l,6-tertiary butyl phenol, cannot be preferentially adsorbed from admixture with thiophenol by this process; it is the 'thiophenol which is adsorbed. substituted and the phenol is not, sharp adsorption of the phenol is aided.

In a similar manner, other mononuclear phenols, such as 0-, m-, or pmono n-butyl phenol are separable from corresponding mono n-butyl thiophenols. 'The compounds are-of very similar structure, molecular weight and'chemical reactivity, but the OH group of the phenol is free and the phenol can be adsorbed-out of mixtures. Various propyl and isopropyl phenols are common and can be separated from corresponding thiophenols-by adsorption in accordance with the process described. Xylenols constitute another type of phenol which is readily separated from admixture with thiophenols. Thus, the various xylenols, some of which occur in mixtures such as the acid oils mentioned, are readily separated from thiophenols or their corresponding thioxylenols, because the OH group of the xylenol is -essentially unhindered and available for adsorption.

It will be seen, ;-therefore, that I have found a simple method for separating phenols from thiophenols. Similar tests made with activated charcoal and activated alumina indicated that neither of these materials was effective to separate thiocresols from cresols.

What is claimed is:

1. The method of separating a mixture of phenols and thiophenols of similar structure into at least two fractions, the phenol being soluble in caustic alkali solution of about 10 per cent concentration, one of which is richer in phenols and the other of which is richer in thiophenols than the original mixture comprising, contacting the mixture with silica gel, removing the unadsorbed mixture from the silica gel and then solvent extracting a mixture richer in phenols from the silica gel.

2. Method in accordance with claim 1 in which the unadsorbed mixture is removed from the silica gel by washing it with a low-boiling hydrocarbon solvent and the fraction richer in phenols is extracted from the silica gel with a low-boiling ketone.

3. The method in accordance with claim 1 in which the fraction richer in phenols is extracted from the silica gel with acetone.

If the thiophenol is highly 4. The method in accordance with claim 1 in which the fraction richer in phenols is extracted from the silica gel with butanone.

5. The method in accordance with claim 1 in which the mixture is an acid oil fraction boiling from about 300 to 450 F.

6. The method of separating a mixture of monohydroxy phenols and thiophenols of similar structure into at least two fractions, the phenol being soluble in caustic alkali of about 10 per cent concentration, one of which is richer in phenols and another of which is richer in thiophenols than the original mixture comprising, percolating a mixture of phenols and thiophenols through a bed of silica gel, removing unadsorbed mixture from said bed and then solvent extracting the adsorbed fraction richer in phenols from the silica gel.

7. The method in accordance with claim 6 in which the mixture is percolated through the bed until the efliuent liquid is of substantially the same composition as the charge.

8. The method in accordance with claim 6 in which the unadsorbed mixture is removed from the silica gel by washing with a low-boiling hydrocarbon solvent and the adsorbed fraction richer in phenols is removed from the silica gel by extraction with a low-boiling ketone.

9. Method in accordance with claim 8 in which the ketone is acetone.

10. Method in accordance with claim 8 in which the ketone is butanone.

11. The method of separating monohydroxy mononuclear phenols from thiophenols of closely related structure comprising, percolating a mixture of phenols and thiophenols through a bed of silica gel until the effluent liquid has substantially the same composition as the charging mixture, washing the silica gel with hexane until substantially all unadsorbed mixture is removed and then extracting a fraction richer in phenols than the original mixture from the silica gel with acetone.

12. The method of recovering phenol from a mixture containing phenol and thiophenol comprising, contacting the mixture with silica gel, removing unadsorbed constituents from the silica gel, and then solvent extracting the adsorbed constituents from the silica gel.

13. The method of recovering concentrated cresols from a mixture containing cresols and thiocresols comprising, contacting the mixture with silica gel, removing unadsorbed constituents from the silica gel and then solvent extracting the adsorbed constituents from the silica gel.

14. The method in accordance with claim 13 in which the unadsorbed constituents are removed from the silica gel by washing with a low-boiling hydrocarbon solvent and the adsorbed constituents are removed from the silica gel by extraction with a low-boiling ketone.

15. The method in accordance with claim 13 in which the adsorbed constituents are extracted with acetone.

16. The method in accordance with claim 13 in which the adsorbed constituents are extracted with butanone.

17. The method of obtaining concentrated cresols from a mixture of cresols and thiocresols comprising, percolating said mixture through silica gel until the composition of the efiluent is substantially the same as the charging mixture, washing the silica gel with hexane until substantially all hexane-extractable material is removed, then washing the silica gel with acetone and separating the acetone from the material extracted from the silica gel.

18. The method in accordance with claim 1 in which the mixture is contacted with silica gel at approximately atmospheric temperature.

19. The method in accordance with claim 11 in which the mixture is contacted with silica gel at approximately atmospheric temperature.

HANS SCHINDLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,537,260 Patrick May 12, 1925 1,882,146 Holmes Oct. 11, 1932 2,098,779 Gericke et al. Nov. 9, 1937 2,343,165 Adler Feb. 29, 1944 

